This invention relates to an image processing apparatus, wherein pictures are processed in accordance with the condition of image signals, particularly to the ones which are incorporated with a function of image's gamma correction.
The conventional method of making gamma corrections and controlling brightness is to control the gradient of a gamma function which is usually linear so as to make the signal upper limit value coincide with the highest possible brightness according to the brightness in image's central area. This method is employed in an automatic iris of a video camera. As illustrated in FIG. 15(A), the gradient of a gamma function is controlled by changing the light quantity passing through a controlled opening of the iris and the maximum brightness in image's central area is made to coincide with the maximum available output of the camera so that the image signals in image's central area are well within the dynamic range of the camera.
However, when the aforementioned method is used in taking pictures of a shaded object standing with its back against a bright background, the gradient of gamma function is adjusted by making the maximum brightness in image's central area coincide with the maximum possible output signal of the camera by opening the camera iris larger than usual and, as illustrated in FIG. 15(B), the pictures of the bright background turn out white all over due to the saturation of the output signal of the camera.
This invention is intended for solving the foregoing problem by providing an image processing apparatus wherein the best possible gamma correction is made against whatever picture objects.